Various apparatus have been proposed for preventing injury due to drains in fluid-containing vessels, such as pools and spas, including those which sense a pressure change in the conduit extending from the drain to the pump that draws water from the drain and through the conduit. In response to pressure changes indicating an obstruction of the drain, prior art devices exist which reduce vacuum present in the drain-to-pump conduit by, e.g., turning the pump off and/or opening the conduit to the atmosphere. Notwithstanding, there is a need for improved drain safety protection devices that are operational for different types of drain installations, e.g., those on above-ground and below-ground pools and spas, as well as protection devices which do not interfere with the normal operation of fluid circulation systems as are typically encountered in pools and spas, e.g., during the normal cycling of filter/pump systems on and off, during the establishment of prime condition and during speed changes for pumps. Further, due to laws pertaining to the running of pumps at higher and lower rates of speed to increase economical operation and diminish the use of electricity, it is desirable to have a drain safety protection device that is capable of maintaining safety through speed changes.